The present invention relates generally to the etching of anti-reflective coatings.
The requirements for high density, high performance ultra-large scale integrated semiconductor devices place unique demands on the conductive patterns used in such devices, including, for example, increasingly denser arrays with minimal spacing between conductive lines. The demands for such devices have increased with the advent of sub-half micron manufacturing technology.
Photolithography represents one technique which typically is used in the fabrication of such devices. Anti-reflective coatings (ARCs) are sometimes incorporated into a device to reduce notching caused by reflections of the photolithographic light source from previously-formed device features. Thus, for example, in i-line photolithography, an i-line photoresist can be applied over a dielectric layer, such as an oxide or nitride layer, with an organic ARC formed between the photoresist and the dielectric layer.
To transfer a pattern from a photolithographic mask to a dielectric or other underlayer disposed beneath an ARC, the ARC layer must be etched or removed selectively. Preferably, etching of the ARC should be completed prior to significant etching of the underlayer. That permits subsequent etching of the underlayer subsequently to be carried out in a uniform and controlled manner.
Several techniques have been used to etch the ARC. Those processes, however, have presented various difficulties. For example, some techniques tend to etch the sidewalls of the photoresist pattern as well as the ARC, thereby resulting in a deterioration and widening of critical dimensions formed in the underlayer. Other techniques can etch an oxide or nitride underlayer, as well as the ARC. If the latter techniques are used, the depth of the etch through the ARC and into the oxide or nitride layer will vary depending on variations in pattern density and the dimensions of the device features. The subsequently-etched underlayer exhibits variations in the etch profiles as a result of exposure to different etching chemistries. Such variations in the depth of the etch make the fabrication process more difficult to control and lead to the formation of non-uniform device features.
In general, a technique is disclosed for removing regions of an anti-reflective coating so that a more uniform and controlled etch of an underlayer can subsequently be performed. The disclosed technique is particularly useful for etching organic or organometallic anti-reflective layers, but can be used to etch other anti-reflective layers as well. In addition, the techniques are particularly advantageous for etching anti-reflective coatings disposed on certain oxide and nitride layers, although the underlayer can be formed of other materials as well.
According to one aspect, a method of removing regions of an anti-reflective coating includes etching the anti-reflective coating with a fluorinated hydrocarbon-based plasma etch and etching the anti-reflective coating with an oxygen-based plasma etch. In some implementations, it is advantageous to perform the fluorinated hydrocarbon-based plasma etch first, and subsequently to perform the oxygen-based plasma etch.
In various implementations, the method includes one or more of the following features. If the anti-reflective coating is disposed on an underlayer, the fluorinated hydrocarbon-based plasma etch can be halted prior to any etching of the underlayer. The fluorinated hydrocarbon-based plasma etch can be performed, for example, for a pre-selected duration. The oxygen-based plasma etch then can be performed to expose regions of the underlayer below the anti-reflective coating.
Alternatively, if the fluorinated hydrocarbon-based plasma is capable of etching the underlayer, etching of a portion of the underlayer can be detected during performance of the fluorinated hydrocarbon-based plasma etch, and the fluorinated hydrocarbon-based plasma etch can be halted after etching of the underlayer is detected. In yet other implementations, near-completion of the etching of the anti-reflective coating can be detected, and the fluorinated hydrocarbon-based plasma etch then can be halted. Etching of the underlayer and/or the near-completion of etching of the anti-reflective coating can be detected, for example, through optical or residual gas analysis techniques.
In some implementations, a photoresist mask pattern can be provided on the anti-reflective coating to define the regions of the anti-reflective coating to be removed. The etching steps can be performed, for example, by reactive ion etch processes.
As previously noted, the anti-reflective coating can include an organic or organometallic material. Etching the anti-reflective coating with a fluorinated hydrocarbon can include, for example, providing a gaseous flow of one or more of carbon tetrafluoride (CF4), perfluoro ethane (C2F6), and trifluoromethane (CHF3). Other gases also can be used.
The techniques described above can be used, for example, to fabricate an integrated electrical device including a first layer. The method can include depositing an anti-reflective coating on the first layer and forming a mask pattern, such as a photoresist mask pattern, on the anti-reflective coating. The anti-reflective coating can be etched with a fluorinated hydrocarbon-based plasma etch and subsequently etched with an oxygen-based plasma etch to expose regions of the first layer. The exposed regions of the first layer then can be etched.
Other features and advantages will be readily apparent from the following description, the accompanying drawings, and the claims.